Modified waterborne polyurethane emulsion

Abstract

The invention discloses a modified waterborne polyurethane emulsion, and belongs to the field of waterborne polyurethane. In order to solve the problems that existing waterborne polyurethane is poor in flame retardance and depends on non-renewable energy sources, the modified waterborne polyurethane emulsion is provided and comprises the following components in parts by weight: 15-25 parts of a bio-based emulsifier, 8-15 parts of pentaerythritol, 20-30 parts of isophorone diisocyanate, 80-120 parts of deionized water and a plurality of functional aids, wherein the bio-based emulsifier is a mixed solution of tung oil, glycerol and a first catalyst; the functional additive comprises a chain extender, a second catalyst, a neutralizer and an inorganic flame retardant. The tung oil is used as a biomass core raw material and is subjected to esterification reaction with glycerol to prepare a bio-based emulsifier, and pentaerythritol is combined to construct a full-bio-based polyol system, so that 100% replacement of a petroleum-based raw material is realized, and fossil energy consumption and pollution are reduced from the source; the inorganic flame retardant is matched with other components, so that efficient flame retardance is realized.

Description

Technical Field

[0001] This invention belongs to the field of waterborne polyurethane, and more specifically, relates to a modified waterborne polyurethane emulsion. Background Technology

[0002] Waterborne polyurethane (WPU) is a high-performance polymer material widely used in packaging, furniture finishing, adhesives, and leather processing due to its excellent wear resistance, scratch resistance, and mechanical strength. However, currently, WPU production is highly dependent on non-renewable petroleum resources, and the synthesis process releases harmful pollutants, posing a dual threat to the ecological environment and human health. More importantly, most waterborne polyurethane adhesives on the market lack flame retardancy, and the low ignition point of ordinary polyurethane itself greatly limits the application scenarios and practical value of waterborne polyurethane emulsions. In other words, the raw materials for waterborne polyurethane mainly come from non-renewable petroleum fossil energy, and the synthesis process generates polluting waste, harming the environment and humans. Even with attempts to partially or completely replace petroleum-based raw materials with environmentally friendly and renewable biomass resources, problems such as insufficient bio-based content and unsatisfactory flame retardant performance remain, making it difficult to meet higher environmental protection requirements. Meanwhile, existing technologies typically employ the addition of flame retardants to improve the flame retardant properties of polyurethane emulsions. However, this method requires a large amount of flame retardants and suffers from poor compatibility, affecting the mechanical properties, toughness, and other properties of the polyurethane emulsion. Therefore, how to improve the flame retardant properties of waterborne polyurethane while maintaining good mechanical strength and environmental stability remains a core challenge that urgently needs to be overcome in current research.

[0003] For example, Chinese patent application CN201210559755.6, published on April 24, 2013, discloses a method for preparing tung oil-based flame-retardant polyurethane elastomers, belonging to the field of polymer synthesis chemistry. Using inexpensive and renewable tung oil as a raw material, hydroxylated tung oil is prepared by exchanging it with trimethylolpropane ester. The hydroxylated tung oil then undergoes a double-bond addition reaction with the flame retardant DOPO at 120–200℃ to obtain flame-retardant modified tung oil. This modified tung oil is then reacted with diisocyanate, and a certain amount of 200–500 mesh expandable graphite is added to prepare the tung oil-based flame-retardant polyurethane elastomer. The polyurethane elastomer obtained by this invention is not only low in cost but also has good flame-retardant properties. The drawback of this patent is that the large DOPO structure is chemically bonded to the polyurethane molecular chain, leading to increased material hardness, decreased elasticity, and poor low-temperature toughness, sacrificing mechanical properties.

[0004] For example, Chinese patent application number CN202411493891.9, published on March 11, 2025, discloses a bio-based polyurethane coating and its preparation method, belonging to the field of coating technology. This bio-based polyurethane coating comprises the following raw materials in parts by weight: 100 parts vegetable oil polyol, 70 parts isocyanate... 120 parts, flame retardant 10 25 parts, organic solvent 30 40 parts, catalyst 1 5 parts, hydrophilic chain extender 10 30 portions, neutralizing agent 10 30 portions, deionized water 20 40 parts. Plant polyols, isocyanates, flame retardants, organic solvents, and catalysts are added to a container and mixed to obtain a prepolymer mixture. Then, a hydrophilic chain extender is added, and the mixture is further mixed to obtain a polymer mixture. After cooling, a neutralizing agent is added for neutralization, followed by the addition of deionized water to emulsify and form a polyurethane emulsion. Vacuum distillation yields the bio-based polyurethane coating. The drawback of this patent is the high dosage of the hydrophilic chain extender, which makes the film prone to whitening, swelling, and even re-emulsification upon contact with water after film formation, resulting in very poor water resistance and media resistance of the coating film. Summary of the Invention

[0005] 1. The problem to be solved To address the issues of poor flame retardancy and reliance on non-renewable energy sources in existing waterborne polyurethane emulsions, this invention provides a modified waterborne polyurethane emulsion. This invention uses tung oil as the core biomass raw material, prepares a bio-based emulsifier through esterification with glycerol, and then combines it with pentaerythritol to construct a fully bio-based polyol system, achieving 100% replacement of petroleum-based raw materials, reducing fossil energy consumption and pollution at the source. Furthermore, through the synergistic effect of inorganic flame retardants and other components, highly efficient flame retardancy is achieved. The entire modified waterborne polyurethane emulsion reduces dependence on petroleum resources from the source, using renewable biomass raw materials, which aligns with green chemistry principles. Simultaneously, it ensures that while improving flame retardant performance, the mechanical properties of the emulsion are not damaged.

[0006] 2. Technical Solution To solve the above problems, the present invention adopts the following technical solution.

[0007] A modified waterborne polyurethane emulsion comprises the following components in parts by weight: 15-25 parts of bio-based emulsifier, 8-15 parts of pentaerythritol, 20-30 parts of isophorone diisocyanate, 80-120 parts of deionized water, 5-13 parts of chain extender, 5-15 parts of viscosity reducer, 3-6 parts of neutralizer, and 0.1-0.5 parts of second catalyst; The bio-based emulsifier comprises the following raw materials in parts by weight: tung oil: 30-50 parts; glycerol: 10-20 parts; first catalyst: 0.3-0.8 parts; It also includes an inorganic flame retardant, wherein the inorganic flame retardant accounts for 3 to 12% of the total weight of the modified waterborne polyurethane emulsion; and the inorganic flame retardant is boric acid. The preparation method of the modified waterborne polyurethane emulsion includes the following steps: S1: Preparation of bio-based emulsifiers; wherein: S11: Preheat the mixture of tung oil, glycerol and the first catalyst in an oil bath at a temperature of 200-260°C. S12: After preheating, the mixture is reacted at a constant temperature of 160~190℃ until the product turns golden yellow and there is no precipitate. The reaction is then stopped to obtain a bio-based emulsifier. S2: Bio-based emulsifier, pentaerythritol and isophorone diisocyanate are mixed and reacted to obtain a mixture; the mixing reaction parameters are: prepolymerization at 85~95℃ for 0.5h~1h; S3: Add a second catalyst to the mixture and react at the first reaction temperature for the first time; S4: Add chain extender to the mixture and react at the second reaction temperature for the second time; S5: Add a neutralizing agent to the mixture and react at the third reaction temperature for the third time; S6: At room temperature, add deionized water to the mixture and react for the fourth time. S7: Add flame retardant to the mixture and physically blend until homogeneous to obtain a modified waterborne polyurethane emulsion; wherein: The first reaction temperature is 95~105℃ and the first reaction time is 2.5~3.5 h; the second reaction temperature is 65~75℃ and the first reaction time is 1.5~2.5 h; the second reaction temperature is 35~45℃ and the first reaction time is 30min~50min; the fourth reaction time is 25min~35min.

[0008] Furthermore, the chain extender comprises the following raw materials in parts by weight: 3 to 8 parts of hydrophilic chain extender and 2 to 5 parts of small molecule chain extender.

[0009] Furthermore, the hydrophilic chain extender is dimethylolpropionic acid, the small molecule chain extender is 1,4-butanediol, the viscosity reducer is N-methylpyrrolidone, the neutralizing agent is triethylamine, and the second catalyst is dibutyltin dilaurate.

[0010] Furthermore, when the chain extender includes a hydrophilic chain extender and a small molecule chain extender, the hydrophilic chain extender is added in step S3, and the small molecule chain extender is added in step S4.

[0011] 3. Beneficial effects (1) This invention first uses tung oil, a renewable vegetable oil, as the core biomass source. Utilizing the three conjugated double bonds and ester bonds in its molecular structure, it undergoes an esterification reaction with glycerol under the catalysis of a first catalyst. This results in more thorough ester exchange, and the conjugated system promotes char formation upon heating, enhances molecular chain rigidity, and improves flame retardancy and heat resistance. During heating, it can self-crosslink and polymerize, forming an additional crosslinking network in WPU film formation, thus improving film performance. Tung oil replaces polyols prepared from traditional petroleum fossil energy, effectively reducing dependence on non-renewable petroleum fossil energy and minimizing environmental pollution, achieving the goal of environmental protection. Furthermore, there is a synergistic flame-retardant effect between tung oil and inorganic flame retardants. When heated, the char layer formed by tung oil and the inorganic flame retardant together construct a dense barrier layer, effectively inhibiting flame spread and heat transfer, resulting in a limiting oxygen index (LOI) of over 26.5%, which is superior to the 2% based on soybean oil system. The 4.0% increase significantly improves the fire safety of the material. Secondly, pentaerythritol is introduced as a crosslinking monomer, reacting with isophorone diisocyanate to form a biomass-based WPU backbone structure. Pentaerythritol, as a high-functionality (tetrahydroxy) polyol, increases the crosslinking density of the polymer, thereby enhancing the mechanical properties of the emulsion. Its numerous hydroxyl groups form the "carbon source" base group for the intumescent flame-retardant char layer, synergistically working with the inorganic flame retardant as an "acid source" to form an intumescent char layer upon heating, achieving highly efficient flame retardancy. This chemical bonding method avoids the poor compatibility and easy migration problems common with physically added flame retardants, ensuring the long-term stability of the emulsion. The entire modified waterborne polyurethane emulsion reduces dependence on petroleum resources from the source, using renewable biomass raw materials, which aligns with green chemistry principles. Simultaneously, it ensures that while improving flame retardant performance, it avoids damage to the mechanical properties of the emulsion. (2) In addition to the functional additives, this invention also adds a viscosity reducer. This is because pentaerythritol is introduced into the raw materials. As a high-functionality crosslinking monomer, pentaerythritol will significantly increase the branching structure and crosslinking density of the polymer. At the same time, tung oil can also undergo self-crosslinking during film formation and heating in the later stages. While these raw materials improve the performance of the final film, they also make the polymer molecular chains have a stronger tendency to connect with each other during synthesis and storage, resulting in a sharp increase in the viscosity of the system. The addition of the viscosity reducer ensures that even if the molecular chains continue to grow and the degree of branching increases in the subsequent synthesis reaction stages, the viscosity of the entire emulsion system remains low. The temperature can also be maintained within a controllable range; during product storage, it can inhibit the occurrence of particle aggregation and cross-linking reactions, thereby preventing gelation during storage and greatly improving the storage stability of the product; and the weight parts of each functional additive are limited to achieve a balance between molecular structure design, process control, and system stability, so as to achieve excellent flame retardant and mechanical properties using tung oil and pentaerythritol while ensuring the controllability of the synthesis process and the stability of the emulsion product; furthermore, a correlation is established between the weight parts of inorganic flame retardants and the total weight parts of the waterborne polyurethane emulsion. (3) The chain extender in this invention introduces hydrophilic chain extender and small molecule chain extender. The hydrophilic chain extender introduces hydrophilic groups, which, after being neutralized, make the polymer chain hydrophilic, thus enabling it to spontaneously emulsify and disperse into stable microspheres in the aqueous phase. This is the key to achieving water-based emulsion and obtaining a stable emulsion for storage. The small molecule chain extender enhances the hard segment structure and improves mechanical properties. It avoids the limitations of the existence of a single chain extender, ensuring that the emulsion has excellent dispersion stability while possessing high mechanical strength and durability. At the same time, zinc borate is clearly used as an inorganic flame retardant. In this system, the decomposition products of zinc borate can catalyze and strengthen the char layer formed by tung oil and pentaerythritol, making it denser and stronger, achieving better heat and material insulation effects, and promoting the formation of a strong char layer. Through systematic material design and component synergy, zinc borate is freed from its traditional auxiliary role, achieving a high-efficiency flame retardant effect with low addition amount, thereby solving the problem of poor compatibility between traditional flame retardants and petroleum-based WPU. While improving flame retardant performance, it avoids damage to the mechanical properties of the emulsion. (4) The preparation method of the present invention uses high-temperature preheating to allow isophorone diisocyanate to fully react with bio-based emulsifiers, pentaerythritol and other polyols. The high temperature ensures high reactivity, which is beneficial to establish polymer skeleton in a short time. The use of medium-temperature chain extension provides a better reaction rate, which can not only ensure the efficient reaction between small molecule chain extenders and prepolymers, significantly improve the polymer molecular weight, but also effectively inhibit the side reaction between -NCO groups and already formed carbamate bonds at high temperature (such as the formation of urethane esters), avoiding unnecessary branching and crosslinking, which can lead to excessively wide molecular weight distribution or gelation. The use of low-temperature neutralization can avoid localized neutralization. Overheating stabilizes the reaction, and more importantly, low temperature greatly suppresses the side reaction between residual -NCO groups and water, preventing premature CO2 bubble formation that could lead to emulsion demulsification or storage instability. It transforms the polymer from hydrophobic to hydrophilic, laying the foundation for efficient emulsification in the next step and ensuring the chemical stability of the emulsion. Room temperature emulsification helps to quickly "freeze" this stable microstructure after emulsion formation, resulting in an emulsion with uniform particle size distribution and good stability. This preparation method controls the entire reaction process through stepwise cooling; the process is simple, feasible, easy to operate, and readily suitable for industrial production, achieving a balance between product performance and stability. Detailed Implementation

[0012] The present invention will be further described below with reference to specific embodiments.

[0013] A modified waterborne polyurethane emulsion comprises the following components in parts by weight: 15-25 parts of bio-based emulsifier, 8-15 parts of pentaerythritol, 20-30 parts of isophorone diisocyanate, 80-120 parts of deionized water, and several parts of functional additives; wherein the bio-based emulsifier is a mixture of tung oil, glycerol, and a first catalyst; the functional additives include chain extenders, a second catalyst, a neutralizer, and an inorganic flame retardant.

[0014] The core innovation in this embodiment is the reform of the raw material system, replacing reliance on petroleum-based sources: abandoning traditional petroleum-based polyols, tung oil is used as the core biomass raw material. A bio-based emulsifier is prepared through esterification with glycerol, and then combined with pentaerythritol to construct a fully bio-based polyol system, 100% replacing petroleum-based raw materials. This reduces fossil fuel consumption and pollution emissions at the source, and the raw material cost is lower and the sources are more diverse. Specifically, tung oil, a renewable vegetable oil, is used as the core biomass source, utilizing its three conjugated double bonds and ester bonds in its molecular structure. It contains active groups and has higher reactivity than soybean oil. It undergoes esterification with glycerol under sodium methoxide catalysis, resulting in more thorough transesterification. The conjugated system can promote char formation upon heating, enhance molecular chain rigidity, and improve flame retardancy and heat resistance. It can also self-crosslink polymerize upon heating, forming an additional crosslink network in WPU film formation, thus improving film performance. This is something that castor oil and other similar products do not possess. In addition, tung oil can synergistically retard flame with inorganic flame retardants such as zinc borate, constructing a barrier layer with an LOI value of over 26.5%, which is superior to the 24.0% of the soybean oil system. The raw material formulation also incorporates pentaerythritol as a crosslinking monomer, which reacts with isophorone diisocyanate (IPDI) to form a biomass-based WPU backbone structure. As a highly functional (tetrahydroxy) polyol, pentaerythritol can increase the crosslinking density of the polymer, thereby improving its mechanical properties. Its numerous hydroxyl groups can form the basic "char source" component of the intumescent flame-retardant char layer, synergistically forming char with inorganic flame retardants such as zinc borate as an "acid source," avoiding the disadvantages of poor compatibility and easy migration of physically added flame retardants. This reduces the consumption of petroleum resources from the source, and the synthesis process generates no additional polluting waste. Regarding flame retardant performance: there is a synergistic flame retardant effect between tung oil and inorganic flame retardants; in addition, pentaerythritol is introduced as a crosslinking monomer. The abundant hydroxyl groups of pentaerythritol can serve as the basic component of the "char source" in the intumescent flame retardant system. It works synergistically with inorganic flame retardants as "acid sources" to form an intumescent char layer when heated, achieving high-efficiency flame retardancy; these synergies enable inorganic flame retardants to overcome the bottleneck of "performance degradation caused by adding large amounts of flame retardants", and achieve low-addition inorganic flame retardants. They can be physically blended without high-load flame retardants. While ensuring compatibility with WPU emulsion, the LOI reaches more than 30%, which solves the contradiction between flame retardancy and mechanical properties.

[0015] In other words, this embodiment addresses the bottlenecks commonly found in existing WPUs, such as "increased flame retardancy leads to decreased mechanical properties" and "a contradiction between environmental degradability and adhesive strength." It achieves synergistic performance through multi-dimensional regulation: Regarding flame retardancy, by adding inorganic flame retardants and co-producing them with other raw materials, a low-dose addition is achieved while maintaining a stable limiting oxygen index (LOI) of over 30%, far exceeding the low ignition point of ordinary WPUs, without relying on large doses of flame retardants. Regarding degradability, leveraging the natural degradability of bio-based emulsifiers, after 180 days of composting (58±2℃, 58±5% humidity), the degradation rate of the pure adhesive-cured film is ≥92%, and it passes the ASTM D6866 bio-based carbon content test and OECD... The 208 / 221 ecotoxicity test shows no ecological risk, solving the environmental problem of existing WPU's difficulty in degradation. In terms of adhesive strength, by precisely controlling the coating thickness (0.1mm) and curing conditions (23℃ / 24h), combined with a peel test speed of 30mm / min on a universal testing machine, the peel strength between leather and plastic parts (ABS, PVC) is ≥20N / 25mm. At the same time, through rotational viscometer testing (25±1℃, 60rpm), the emulsion viscosity is ensured to meet the construction requirements of roller coating / spraying (coating amount 10~15g / m²), achieving a synergistic performance of "flame retardant-degradable-high strength-easy construction".

[0016] In one specific embodiment, the functional additives further include a viscosity reducer; and the weight parts of each functional additive are as follows: chain extender 5-13 parts; viscosity reducer 5-15 parts; neutralizer 3-6 parts; second catalyst 0.1-0.5 parts; and the weight parts of the inorganic flame retardant account for 3-12% of the total weight parts of the waterborne polyurethane emulsion.

[0017] This embodiment particularly emphasizes that the amount of inorganic flame retardant is not a fixed value, but rather is related to the total weight percentage of the waterborne polyurethane emulsion. This is because current technologies typically require large amounts of flame retardant, which inevitably leads to excessive dilution of the resin matrix, severely disrupting the continuity of the polymer network and causing a sharp decline in the mechanical properties (such as tensile strength, elongation at break), flexibility, and transparency of the film. This presents a technical bottleneck where flame retardancy is improved at the expense of mechanical properties. Therefore, this embodiment first optimizes the raw material design by introducing tung oil and pentaerythritol. Tung oil and pentaerythritol have a highly efficient "char source" foundation built into the polymer chain. Under this premise, only 3-12% zinc borate is needed as an "acid source" and synergist to achieve a significant "catalytic-synergistic" flame retardant effect with the biomass components. In this system, the decomposition products of zinc borate catalyze and strengthen the char layer formed by tung oil and pentaerythritol, making it denser and stronger, resulting in better thermal and thermal insulation and promoting the formation of a robust char layer. Through systematic material design and component synergy, zinc borate has broken free from its traditional auxiliary role, achieving high-efficiency flame retardant effects with low addition levels. This solves the problem of poor compatibility between traditional flame retardants and petroleum-based WPU, improving flame retardant performance while avoiding damage to the mechanical properties of the emulsion.

[0018] Secondly, the specific numerical range is limited to 3-12%. This is because when the dosage is below 3%, the flame retardant effect will be insufficient; when the dosage is above 12%, the excessive inorganic particles will increase the risk of agglomeration and sedimentation due to the high surface energy. This will not only easily cause problems such as delamination and blockage during storage and construction, but will also act as stress defect points after film formation, seriously deteriorating the film's density, hydrolysis resistance, and mechanical strength. Therefore, a suitable range is determined to achieve a balance between flame retardancy and mechanical properties.

[0019] More specifically, the chain extender comprises the following raw materials in parts by weight: 3-8 parts of hydrophilic chain extender and 2-5 parts of small molecule chain extender. This embodiment employs a design with two chain extenders: the hydrophilic chain extender's main function is to introduce hydrophilic groups (carboxyl groups), which is crucial for achieving water-based emulsions and obtaining storage-stable emulsions; the small molecule chain extender's main function is to enhance the hard segment structure and improve mechanical properties. As a short-chain diol, the small molecule chain extender can react with isocyanate (IPDI) to effectively form regular, dense urea bonds and urethane bonds in the polymer chain. These strongly polar groups form physical crosslinking points through hydrogen bonding, greatly improving the tensile strength, hardness, abrasion resistance, and heat resistance of the film. The two chain extenders each perform their respective functions, overcoming the performance defects of a single chain extender, ultimately achieving excellent dispersion stability in the emulsion while possessing outstanding mechanical strength and durability.

[0020] The hydrophilic chain extender is dimethylolpropionic acid, the small molecule chain extender is 1,4-butanediol, the viscosity reducer is N-methylpyrrolidone, the neutralizing agent is triethylamine, the second catalyst is dibutyltin dilaurate, and the inorganic flame retardant is zinc borate. It is worth noting that zinc borate was chosen as the inorganic flame retardant because of its excellent synergistic effect with the "char source" formed by tung oil and pentaerythritol. When heated, it can act as an "acid source" to promote char formation and also form a glassy coating layer. Together with the char layer formed by tung oil, it constructs a robust expansion barrier layer, achieving low-dose addition.

[0021] In one specific embodiment, the bio-based emulsifier comprises the following raw materials in parts by weight: tung oil: 30-50 parts; glycerol: 10-20 parts; catalyst: 0.3-0.8 parts.

[0022] A method for preparing a modified waterborne polyurethane emulsion as described in any of the above embodiments includes the following steps: S1: Preparation of bio-based emulsifiers; specifically, in this embodiment, it is as follows: S11: Preheat the mixture of tung oil, glycerol and the first catalyst in an oil bath at a temperature of 200-260°C. S12: After preheating, the mixture is reacted at a constant temperature of 160~190℃ until the product turns golden yellow and there is no precipitate. The reaction is then stopped to obtain a bio-based emulsifier. S2: A mixture of bio-based emulsifier, pentaerythritol, and isophorone diisocyanate is reacted to obtain a mixture; the reaction parameters are prepolymerization at 85~95℃ for 0.5h~1h. S3: Add a second catalyst to the mixture and react at the first reaction temperature for the first time; S4: Add chain extender to the mixture and react at the second reaction temperature for the second time; S5: Add a neutralizing agent to the mixture and react at the third reaction temperature for the third time; S6: At room temperature, add deionized water to the mixture and react for the fourth time. S7: Add flame retardant to the mixture and physically blend until homogeneous to obtain a modified waterborne polyurethane emulsion; wherein: First reaction temperature > Second reaction temperature > Third reaction temperature > Room temperature; First reaction duration > Second reaction duration > Third reaction duration > Fourth reaction duration.

[0023] Specifically, the first reaction temperature is 95~105℃ and the first reaction time is 2.5~3.5 h; the second reaction temperature is 65~75℃ and the first reaction time is 1.5~2.5 h; the second reaction temperature is 35~45℃ and the first reaction time is 30min~50min; the fourth reaction time is 25min~35min.

[0024] It is worth noting that in this embodiment, step S4 mainly involves a chain extension reaction, step S5 mainly involves a neutralization reaction, and step S6 mainly involves an emulsification reaction. Setting it to a stepped temperature control is primarily to avoid main chain breakage due to localized overheating or performance defects caused by incomplete reaction. Specifically, this is based on the following considerations: During the chain extension reaction, the temperature is lowered from 95~105℃ to 65~75℃. This stage is the chain extension reaction and viscosity control stage. Controlling the reaction within this temperature range results in an optimal reaction rate, ensuring chain extension efficiency while avoiding excessive side reactions (such as the formation of urethane esters). The viscosity of the prepolymer increases as the temperature decreases. At 65~75℃, the system still maintains good fluidity, facilitating the uniform mixing and reaction of BDO. At the same time, the addition of NMP at this temperature has the most significant viscosity-reducing effect, effectively preventing the risk of gelation caused by molecular chain growth. This achieves linear growth of the molecular chain, significantly increasing the polymer molecular weight and providing the film with excellent mechanical strength and toughness.

[0025] During the neutralization reaction, the temperature is lowered from 65-75℃ to 35-45℃. This stage is crucial for both neutralization and stability preparation. The neutralization of the carboxyl groups (-COOH) of DMPA by triethylamine (TEA) to form a carboxylate is an exothermic reaction. Conducting the reaction at 40℃ allows for stable control of the neutralization process, preventing localized overheating. More importantly, the low temperature significantly suppresses the side reactions between residual -NCO groups and water, preventing premature CO2 bubble formation that could lead to emulsion demulsification or storage instability. This transformation of the polymer from hydrophobic to hydrophilic lays the foundation for efficient emulsification in the next step and ensures the chemical stability of the emulsion.

[0026] During the emulsification reaction, the temperature is lowered from 35-45°C to room temperature. This stage is characterized by rapid emulsification and phase transition. Room temperature emulsification helps to quickly "freeze" this stable microstructure after emulsion formation, resulting in an emulsion with uniform particle size distribution and good stability. This yields an aqueous polyurethane emulsion with stable solid content, uniform particle size, and stable storage.

[0027] Meanwhile, in this embodiment, the inorganic flame retardant is added only through physical blending, without the need for additional reaction steps. This simplifies the process and ensures that the inorganic flame retardant is uniformly dispersed in the emulsion by controlling the stirring rate, further guaranteeing the stability of the product performance.

[0028] In summary, the preparation method of this embodiment precisely controls the emulsion structure through stepwise temperature-controlled reaction and high-speed emulsification process, achieving a peel strength of ≥20N / 25mm, a viscosity suitable for 10-15g / m² roller coating / spraying, and a compost degradation rate of ≥92% in 3 months. It balances adhesion performance, workability, and environmental friendliness, making it suitable for various scenarios such as automotive, aviation, and agricultural product packaging.

[0029] In one specific embodiment, when the chain extender includes a hydrophilic chain extender and a small molecule chain extender, the hydrophilic chain extender is added in step S3, and the small molecule chain extender is added in step S4. The hydrophilic chain extender contains hydrophilic groups such as carboxyl groups (-COOH), which have relatively low reactivity with isocyanate groups (-NCO), requiring higher reaction temperatures and longer reaction times for a complete reaction. In step S3, the initial reaction temperature is high and the initial reaction time is long, providing sufficient energy and time for the hydrophilic chain extender to effectively integrate into the polyurethane chain, thereby introducing hydrophilic groups and laying the foundation for subsequent aqueous dispersion, ensuring uniform carboxyl group introduction. The small molecule chain extender contains hydroxyl groups (-OH), which have high reactivity with -NCO groups and a faster reaction rate. If added simultaneously with the hydrophilic chain extender, the small molecule chain extender may react preferentially, preventing the hydrophilic chain extender from uniformly integrating into the polymer chain, thus affecting the hydrophilicity and stability of the emulsion. Therefore, adding the two at different times ensures the acquisition of a high-performance, stable aqueous polyurethane emulsion.

[0030] To further facilitate understanding of the solution and effects of this application, the following embodiments and comparative examples are provided: Example 1 A modified waterborne polyurethane emulsion comprises the following components in parts by weight: 10 parts pentaerythritol, 25 parts isophorone diisocyanate (IPDI), 20 parts bio-based emulsifier, 5 parts dimethylolpropionic acid (DMPA), 0.3 parts dibutyltin dilaurate (DBTDL), 3 parts 1,4-butanediol (BDO), 10 parts N-methylpyrrolidone (NMP) (viscosity reducer), 4 parts triethylamine (TEA) (neutralizer), 100 parts deionized water, and zinc borate (ZB) in parts by weight for modification. 5% of the total weight of the waterborne polyurethane emulsion, which is 8.865 parts, is: (10+25+20+5+0.3+3+10+4+100)*5%=8.865. However, for the convenience of actual experiments and production, the weight of zinc borate is rounded to the nearest whole number according to the rounding rules. In this embodiment, the weight of ZB is taken as 9 parts. The bio-based emulsifier includes the following raw materials in the following weight parts: 40 parts of tung oil, 15 parts of glycerol, and 0.5 parts of sodium methoxide (first catalyst). The preparation method of the modified waterborne polyurethane emulsion is as follows: Tung oil, glycerol and sodium methoxide were stirred in an oil bath at 220°C at 180°C and 600 r / min for 4 hours to obtain a golden-yellow bio-based emulsifier. Add pentaerythritol, IPDI, and a bio-based emulsifier to a four-necked flask and react at 90°C for 1 hour; add DMPA and DBTDL and react at 100°C for 3 hours; cool to 70°C and add BDO for chain extension for 2 hours, during which NMP is added to reduce viscosity; cool to 40°C and add TEA to neutralize for 40 minutes; add deionized water at room temperature and emulsify at 2000 rpm for 30 minutes. ZB was added to the WPU emulsion and physically blended to obtain a modified waterborne polyurethane emulsion.

[0031] Example 2 A modified waterborne polyurethane emulsion comprises the following components in parts by weight: 10 parts pentaerythritol, 25 parts isophorone diisocyanate (IPDI), 20 parts bio-based emulsifier, 5 parts dimethylolpropionic acid (DMPA), 0.3 parts dibutyltin dilaurate (DBTDL), 3 parts 1,4-butanediol (BDO), 10 parts N-methylpyrrolidone (NMP) (viscosity reducer), 4 parts triethylamine (TEA) (neutralizer), 100 parts deionized water, and zinc borate. The weight percentage of (ZB) is 8% of the total weight percentage of the modified waterborne polyurethane emulsion, which is 14.184 parts, specifically: (10+25+20+5+0.3+3+10+4+100)*8%=14.184. However, for the convenience of conducting experiments in actual practice, the weight percentage of ZB in this embodiment is taken as 14 parts. The bio-based emulsifier includes the following raw materials in the following weight percentages: 40 parts tung oil, 15 parts glycerol, and 0.5 parts sodium methoxide (first catalyst). The preparation method of the modified waterborne polyurethane emulsion is as follows: Tung oil, glycerol and sodium methoxide were stirred in an oil bath at 220°C at 180°C and 600 r / min for 4 hours to obtain a golden-yellow bio-based emulsifier. Add pentaerythritol, IPDI, and a bio-based emulsifier to a four-necked flask and react at 90°C for 1 hour; add DMPA and DBTDL and react at 100°C for 3 hours; cool to 70°C and add BDO for chain extension for 2 hours, during which NMP is added to reduce viscosity; cool to 40°C and add TEA to neutralize for 40 minutes; add deionized water at room temperature and emulsify at 2000 rpm for 30 minutes. ZB was added to the WPU emulsion and physically blended to obtain a modified waterborne polyurethane emulsion.

[0032] Example 3 A modified waterborne polyurethane emulsion comprises the following components in parts by weight: 10 parts pentaerythritol, 25 parts isophorone diisocyanate (IPDI), 20 parts bio-based emulsifier, 5 parts dimethylolpropionic acid (DMPA), 0.3 parts dibutyltin dilaurate (DBTDL), 3 parts 1,4-butanediol (BDO), 10 parts N-methylpyrrolidone (NMP) (viscosity reducer), 4 parts triethylamine (TEA) (neutralizer), 100 parts deionized water, and zinc borate. The weight percentage of (ZB) is 8% of the total weight percentage of the modified waterborne polyurethane emulsion, which is 14.184 parts, specifically: (10+25+20+5+0.3+3+10+4+100)*8%=14.184. However, for the convenience of conducting experiments in actual practice, the weight percentage of ZB in this embodiment is taken as 14 parts. The bio-based emulsifier includes the following raw materials in the following weight percentages: 45 parts tung oil, 12 parts glycerol, and 0.5 parts sodium methoxide (first catalyst). The preparation method of the modified waterborne polyurethane emulsion is as follows: Tung oil, glycerol and sodium methoxide were stirred in an oil bath at 220°C at 180°C and 600 r / min for 4 hours to obtain a golden-yellow bio-based emulsifier. Add pentaerythritol, IPDI, and a bio-based emulsifier to a four-necked flask and react at 90°C for 1 hour; add DMPA and DBTDL and react at 100°C for 3 hours; cool to 70°C and add BDO for chain extension for 2 hours, during which NMP is added to reduce viscosity; cool to 40°C and add TEA to neutralize for 40 minutes; add deionized water at room temperature and emulsify at 2000 rpm for 30 minutes. ZB was added to the WPU emulsion and physically blended to obtain a modified waterborne polyurethane emulsion.

[0033] Example 4 A modified waterborne polyurethane emulsion comprises the following components in parts by weight: 12 parts pentaerythritol, 22 parts isophorone diisocyanate (IPDI), 20 parts bio-based emulsifier, 5 parts dimethylolpropionic acid (DMPA), 0.3 parts dibutyltin dilaurate (DBTDL), 3 parts 1,4-butanediol (BDO), 10 parts N-methylpyrrolidone (NMP) (viscosity reducer), 4 parts triethylamine (TEA) (neutralizer), 100 parts deionized water, and zinc borate. The weight percentage of (ZB) is 7% of the total weight percentage of the modified waterborne polyurethane emulsion, which is 12.341 parts, specifically: (10+25+20+5+0.3+3+10+4+100)*7%=12.341. However, for the convenience of conducting experiments in actual practice, the weight percentage of ZB in this embodiment is taken as 12 parts. The bio-based emulsifier includes the following raw materials in the following weight percentages: 40 parts tung oil, 15 parts glycerol, and 0.5 parts sodium methoxide (first catalyst). The preparation method of the modified waterborne polyurethane emulsion is as follows: Tung oil, glycerol and sodium methoxide were stirred in an oil bath at 220°C at 180°C and 600 r / min for 4 hours to obtain a golden-yellow bio-based emulsifier. Add pentaerythritol, IPDI, and a bio-based emulsifier to a four-necked flask and react at 90°C for 1 hour; add DMPA and DBTDL and react at 100°C for 3 hours; cool to 70°C and add BDO for chain extension for 2 hours, during which NMP is added to reduce viscosity; cool to 40°C and add TEA to neutralize for 40 minutes; add deionized water at room temperature and emulsify at 2000 rpm for 30 minutes. ZB was added to the WPU emulsion and physically blended to obtain a modified waterborne polyurethane emulsion.

[0034] Comparative Example 1 The process is basically the same as in Example 1, except that a traditional petroleum-based emulsifier (alkylphenol polyoxyethylene ether, 10 parts) is used instead of a bio-based emulsifier. All other aspects are the same as in Example 1.

[0035] Comparative Example 2 It is essentially the same as Example 1, except that no bio-based emulsifier or any other type of emulsifier is used. Otherwise, it is the same as Example 1.

[0036] Comparative Example 3 The results are basically the same as in Example 1, except that the components of the bio-based emulsifier are soybean oil (40 parts) and glycerol (15 parts), and the catalyst is sodium methoxide (0.5 parts). All other components are the same as in Example 1.

[0037] Comparative Example 4 The results are basically the same as in Example 1, except that the components of the bio-based emulsifier are reduced to 20 parts of tung oil and increased to 20 parts of glycerol. All other components are the same as in Example 1.

[0038] Comparative Example 5 The process is basically the same as in Example 1, except that the esterification reaction time is shortened to 2 hours during the preparation of the bio-based emulsifier, and the product is not golden yellow and contains precipitate.

[0039] Comparative Example 6 It is basically the same as Example 1, except that no inorganic flame retardant is added to the components. Everything else is the same as Example 1.

[0040] Comparative Example 7 It is basically the same as Example 1, except that aluminum hydroxide flame retardant is used instead of zinc borate flame retardant in the components. Everything else is the same as Example 1.

[0041] Comparative Example 8 It is basically the same as Example 1, except that a phosphate ester flame retardant is used instead of zinc borate flame retardant in the components. Everything else is the same as Example 1.

[0042] Comparative Example 9 The results are basically the same as in Example 1, except that the weight percentage of zinc borate (ZB) is 15% of the total weight percentage of the modified waterborne polyurethane emulsion. All other aspects are the same as in Example 1.

[0043] Comparative Example 10 The results are basically the same as in Example 1, except that the weight of zinc borate (ZB) is 2% of the total weight of the modified waterborne polyurethane emulsion. All other aspects are the same as in Example 1.

[0044] Comparative Example 11 The results are basically the same as in Example 1, except that toluene diisocyanate (TDI) is used instead of isophorone diisocyanate (IPDI) in the components. All other aspects are the same as in Example 1.

[0045] Comparative Example 12 It is basically the same as Example 1, except that bio-based emulsifiers and pentaerythritol are not used in the components, and petroleum-based polyether polyols are used directly. All other aspects are the same as in Example 1.

[0046] Comparative Example 13 The process is basically the same as in Example 1, except that the modified waterborne polyurethane emulsion is prepared by a constant temperature reaction at 80°C throughout, without any step temperature control steps. Pentaerythritol and IPDI are prepolymerized at 80°C for 1 hour, DMPA and DBTDL are added and the reaction continues at 80°C for 3 hours, BDO is added and the chain is extended at 80°C for 2 hours, and finally TEA is added at 80°C for 40 minutes to neutralize. During the emulsification stage, the rotation speed is reduced to 1000 r / min and the emulsification time is 30 minutes. All other steps are the same as in Example 1.

[0047] Comparative Example 14 The process is basically the same as in Example 1, except that in the preparation method of the modified waterborne polyurethane emulsion, pentaerythritol, IPDI and bio-based emulsifier are added to a four-necked flask and reacted at 110°C for 30 min. All other aspects are the same as in Example 1.

[0048] Comparative Example 15 The method is basically the same as in Example 1, except that in the preparation method of the modified waterborne polyurethane emulsion, BDO is added for chain extension for 2 hours when the temperature is lowered to 90°C, and NMP is not added to reduce viscosity during this period. All other aspects are the same as in Example 1.

[0049] Comparative Example 16 The method is basically the same as in Example 1, except that in the preparation method of the modified waterborne polyurethane emulsion, the temperature is lowered to 60°C and TEA is added for neutralization for 20 minutes. The rest is the same as in Example 1.

[0050] Comparative Example 17 The process is basically the same as in Example 1, except that in the preparation method of the modified waterborne polyurethane emulsion, deionized water is added at room temperature and emulsified at 1200 r / min for 15 minutes. All other aspects are the same as in Example 1.

[0051] Comparative Example 18 The method is basically the same as in Example 1, except that in the preparation method of the modified waterborne polyurethane emulsion, the oil bath preheating temperature of the bio-based emulsifier is 200°C, the esterification reaction temperature is 140°C, the stirring rate is 300 r / min, and the reaction time is 6 h. All other aspects are the same as in Example 1.

[0052] The modified waterborne polyurethane emulsions prepared in the examples and comparative examples were tested, and the following test data table (Table 1) was obtained: The test methods and testing standards are as follows: Adhesive Viscosity Performance Testing: The test object is the rheological properties of modified waterborne polyurethane emulsion in liquid state. The purpose of the test is to evaluate the workability and flow properties of the adhesive. The test principle is based on the flow behavior of Newtonian or non-Newtonian fluids under shear stress. The experimental method uses a rotational viscometer at 25±1℃, using a No. 2 rotor at 60 rpm to measure the apparent viscosity of the adhesive. The value is read after stabilizing for 30 seconds. The standard is GB / T 2794-2013 "Determination of Viscosity of Adhesives". Key parameters include test temperature 25±1℃, sample volume 500mL, and rotation speed 60 rpm. Data processing: The viscosity value is directly read to determine whether it is within the process requirements and to evaluate the workability of the adhesive.

[0053] Flame retardancy test requirements: The test object is the flame retardancy performance of pure glue-cured samples of water-based polyurethane emulsion adhesive. The purpose of the test is to evaluate the flame retardancy performance of the material itself. The test principle is to determine the minimum oxygen concentration (i.e., limiting oxygen index LOI) required to sustain combustion by precisely controlling the oxygen concentration in the material's combustion environment. The higher the LOI value, the less likely the material is to burn in air, and the better its flame retardant performance. The experimental method is based on the national standard GB / T 2406.2-2009, using the oxygen index method: The adhesive is cured and dried to constant weight, and samples with a length of 80-150 mm, a width of 10 mm, and a thickness not exceeding 10.5 mm are prepared. After conditioning in a standard environment of 23±2℃ and 50±5% humidity for at least 88 hours, the samples are vertically fixed in the combustion chamber of an oxygen index tester. A controllable oxygen / nitrogen mixed gas flow is introduced, and the top of the sample is ignited. By adjusting the oxygen concentration, the minimum oxygen volume percentage concentration required for the sample to maintain stable combustion for at least 3 minutes or achieve a burning length of 50 mm is determined. Key parameters include sample size, conditioning environment and time, oxygen concentration conditioning accuracy, and combustion determination conditions. Data processing requires calculating and reporting the measured limiting oxygen index (LOI) value, and evaluating the flame retardancy rating of the material according to relevant standards or technical indicators.

[0054] Biodegradability Test: The test subject is the biodegradation behavior of waterborne polyurethane emulsion adhesive pure adhesive cured film in a composting environment. The purpose of the test is to evaluate the environmental friendliness and biodegradability of the adhesive. The test principle is based on the change in CO2 release caused by the enzymatic hydrolysis and mineralization of organic polymers by microorganisms. Experimental Method: Adhesive samples are prepared into small pieces of 2mm×2mm×0.5mm and subjected to a 180-day degradation test in a composting environment at 58±2℃ and 58±5% relative humidity. The CO2 release and sample mass changes are measured periodically. Cellulose, PLA positive control and PE negative control are set up for comparison. Bio-based carbon content (ASTM D6866) and ecotoxicity (OECD 208 / 221) are also tested. Key parameters include composting temperature 58±2℃, pH value 7.0-9.0, moisture content 50-60%, sample mass 300-500mg, and test period 180 days. Data processing is used to calculate biodegradation rate, biodegradation rate constant, and half-life to evaluate the biodegradation level and environmental safety of materials.

[0055] Peel Strength Test: The test object is the adhesive joint formed at the leather-plastic interface by a water-based polyurethane emulsion adhesive. The purpose of the test is to evaluate the basic adhesive properties and interfacial bond strength of the adhesive. The test principle is based on the mechanical response and failure mechanism of the adhesive joint under peel load. Experimental Method: 25mm × 100mm standard specimens were prepared. The substrates were natural cow leather (1.2mm thick) and PVC artificial leather (surface corona treatment). The adhesive coating thickness was 0.1mm. After curing at 23℃ for 24 hours, a peel test was conducted using a universal testing machine at a tensile speed of 200mm / min. The standard basis is GB / T2792-1998 "Test Method for 180° Peel Strength of Adhesive Tapes". Key parameters include the number of specimens (5), test speed (200mm / min), and curing time (24 hours). Data Processing: The average peel strength was calculated to determine whether the technical requirements were met and to evaluate the bonding quality.

[0056] Table 1 Experimental Data

[0057] As shown in Table 1, Examples 1-4 used tung oil and pentaerythritol to construct a fully bio-based polyol system. The conjugated double bonds of tung oil promote cross-linking and char formation, while pentaerythritol increases the cross-linking density. The two work synergistically to ensure high peel strength (≥26.8 N / 25 mm) and high biodegradability (≥93.3%). Comparative Examples 1 and 12 were replaced with petroleum-based raw materials, and the biodegradability dropped sharply to 39.2%~45.5%, with peel strength less than half that of the examples. Comparative Example 3 used soybean oil instead of tung oil. Due to its low reactivity and poor char formation, the LOI was only 26.5%, far lower than the 31.5%~34.2% of Examples 1-4.

[0058] The stepped temperature control (90℃ prepolymerization, 100℃ reaction, 70℃ chain extension, 40℃ neutralization) and high-speed emulsification (2000r / min) in Examples 1-4 ensured sufficient reaction, uniform emulsion, and viscosity suitable for construction requirements. In contrast, Comparative Examples 13-18, due to deviations in process parameters (constant temperature reaction, improper temperature / speed, insufficient reaction time), all resulted in emulsion gelation, layering, or uneven dispersion, with the lowest peel strength being only 7.6N / 25mm and LOI less than 25%.

[0059] Examples 1-4 used low-dosage zinc borate (ZB) in synergistic flame retardancy with a bio-based system. ZB catalyzed the formation of a dense char layer from tung oil and pentaerythritol, achieving an LOI of 31.5%~34.2%. Comparative Example 6, without flame retardant, had an LOI of only 21.5%. Comparative Examples 7-8 used traditional flame retardants (ATH, phosphate esters), which had poor compatibility and no synergistic effect, resulting in an LOI of less than 26.1% and a sharp drop in peel strength. Comparative Examples 9-10 had inappropriate ZB addition (too much / too little), either causing abnormal emulsion viscosity and decreased strength due to excessive addition, or failing to achieve high-efficiency flame retardancy due to insufficient addition.

[0060] The examples described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention.

Claims

1. A modified waterborne polyurethane emulsion, characterized in that: The product comprises the following components in parts by weight: 15-25 parts bio-based emulsifier, 8-15 parts pentaerythritol, 20-30 parts isophorone diisocyanate, 80-120 parts deionized water, 5-13 parts chain extender, 5-15 parts viscosity reducer, 3-6 parts neutralizer, and 0.1-0.5 parts secondary catalyst. The bio-based emulsifier comprises the following raw materials in parts by weight: tung oil: 30-50 parts; glycerol: 10-20 parts; first catalyst: 0.3-0.8 parts; It also includes an inorganic flame retardant, wherein the inorganic flame retardant accounts for 3 to 12% of the total weight of the modified waterborne polyurethane emulsion; and the inorganic flame retardant is boric acid. The preparation method of the modified waterborne polyurethane emulsion includes the following steps: S1: Preparation of bio-based emulsifiers; wherein: S11: Preheat the mixture of tung oil, glycerol and the first catalyst in an oil bath at a temperature of 200-260°C. S12: After preheating, the mixture is reacted at a constant temperature of 160~190℃ until the product turns golden yellow and there is no precipitate. The reaction is then stopped to obtain a bio-based emulsifier. S2: Bio-based emulsifier, pentaerythritol and isophorone diisocyanate are mixed and reacted to obtain a mixture; the mixing reaction parameters are: prepolymerization at 85~95℃ for 0.5h~1h; S3: Add a second catalyst to the mixture and react at the first reaction temperature for the first time; S4: Add chain extender to the mixture and react at the second reaction temperature for the second time; S5: Add a neutralizing agent to the mixture and react at the third reaction temperature for the third time; S6: At room temperature, add deionized water to the mixture and react for the fourth time. S7: Add flame retardant to the mixture and physically blend until homogeneous to obtain a modified waterborne polyurethane emulsion; wherein: The first reaction temperature is 95~105℃ and the first reaction time is 2.5~3.5 h; the second reaction temperature is 65~75℃ and the first reaction time is 1.5~2.5 h; the second reaction temperature is 35~45℃ and the first reaction time is 30min~50min; the fourth reaction time is 25min~35min.

2. The modified waterborne polyurethane emulsion according to claim 1, characterized in that: The chain extender comprises the following raw materials in parts by weight: 3 to 8 parts of hydrophilic chain extender and 2 to 5 parts of small molecule chain extender.

3. The modified waterborne polyurethane emulsion according to claim 2, characterized in that: The hydrophilic chain extender is dimethylolpropionic acid, the small molecule chain extender is 1,4-butanediol, the viscosity reducer is N-methylpyrrolidone, the neutralizing agent is triethylamine, and the second catalyst is dibutyltin dilaurate.

4. The modified waterborne polyurethane emulsion according to claim 1, characterized in that: When the chain extender includes a hydrophilic chain extender and a small molecule chain extender, the hydrophilic chain extender is added in step S3, and the small molecule chain extender is added in step S4.

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